U.S. patent application number 10/801670 was filed with the patent office on 2004-09-09 for wheeled type working vehicle.
This patent application is currently assigned to Hitachi Construction Machinery Co., Ltd.. Invention is credited to Ichimura, Kazuhiro, Tatsuno, Yukihiro, Tsukui, Hiroshi.
Application Number | 20040173979 10/801670 |
Document ID | / |
Family ID | 27564293 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040173979 |
Kind Code |
A1 |
Ichimura, Kazuhiro ; et
al. |
September 9, 2004 |
Wheeled type working vehicle
Abstract
The wheeled work vehicle according to the present invention has
a link that links at least either one of the axles and provided at
the front and the rear of the vehicle to a body, suspension
hydraulic cylinders provided at the left side and the right side of
the chassis to link the axle to the body in conjunction with the
link and an accumulator that is made to communicate with oil
chambers and of the hydraulic cylinders via restrictors.
Inventors: |
Ichimura, Kazuhiro;
(Niihari-gun, JP) ; Tsukui, Hiroshi; (Abiko-shi,
JP) ; Tatsuno, Yukihiro; (Niihari-gun, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
Hitachi Construction Machinery Co.,
Ltd.
Tokyo
JP
|
Family ID: |
27564293 |
Appl. No.: |
10/801670 |
Filed: |
March 17, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10801670 |
Mar 17, 2004 |
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09890854 |
Aug 7, 2001 |
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09890854 |
Aug 7, 2001 |
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PCT/JP00/00715 |
Feb 9, 2000 |
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Current U.S.
Class: |
280/6.154 |
Current CPC
Class: |
B60G 2204/46 20130101;
B60G 11/30 20130101; B60G 17/005 20130101; B60G 2200/30 20130101;
B60G 2200/341 20130101; E02F 9/2257 20130101; B60G 17/056 20130101;
B60G 2200/32 20130101; B60G 2400/252 20130101; B60G 9/02 20130101;
E02F 9/2217 20130101; B60G 17/015 20130101; B60G 2300/06
20130101 |
Class at
Publication: |
280/006.154 |
International
Class: |
B60G 017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 9, 1999 |
JP |
11-31732 |
Feb 15, 1999 |
JP |
11-36047 |
Feb 15, 1999 |
JP |
11-36048 |
Feb 15, 1999 |
JP |
11-36049 |
Feb 15, 1999 |
JP |
11-36050 |
Feb 9, 1999 |
JP |
11-31733 |
Feb 18, 1999 |
JP |
11-40164 |
Claims
What is claimed is:
1. A wheeled work vehicle, comprising: a link that connects at
least one axle provided at a front and at a rear of said vehicle to
a chassis; hydraulic cylinders for suspension provided at a left
side and a right side of said vehicle, that connect at least one
said axle to said chassis in conjunction with said link; and an
accumulator communicating with oil chambers of said hydraulic
cylinders via restrictors.
Description
INCORPORATION BY REFERENCE
[0001] The disclosures of the following priority applications are
herein incorporated by reference:
[0002] Japanese Patent Application No. H11-031732
[0003] Japanese Patent Application No. H11-036047
[0004] Japanese Patent Application No. H11-036048
[0005] Japanese Patent Application No. H11-036049
[0006] Japanese Patent Application No. H11-036050
[0007] Japanese Patent Application No. H11-031733
[0008] Japanese Patent Application No. H11-040164
BACKGROUND OF THE INVENTION
[0009] 1. Field of Invention
[0010] The present invention relates to a wheeled work vehicle that
travels on tires.
[0011] 2. Description of Related Art
[0012] In order to improve the comfort of the operator driving a
work vehicle travelling on tires such as a wheeled hydraulic
excavator, which has come to run at an increasingly high speed in
recent years, Japanese Laid-Open Patent Publication No.S 62-110509,
Japanese Laid-Open Patent Publication No. H 6-278438, Japanese
Laid-Open Patent Publication No. H 7-125523 and Japanese Laid-Open
Patent Publication No. H 7-132723, for instance, each disclose a
work vehicle having a suspension mechanism provided between the
body and an axle.
[0013] In the work vehicle disclosed in Japanese Laid-Open Patent
Publication No. S62-110509 (hereafter referred to as prior art 1),
two sets of hydraulic cylinders are provided at the two sides,
i.e., on the left side and the right side of the body, the upper
ends of the cylinder tubes and the lower ends of the cylinder rods
are respectively linked to the body and the beam provided over the
axle by using pins, and a long hole extending along the vertical
direction is formed at the center of the body to link the upper
center of the beam and the center of the body with a pin inserted
at the long hole. The head chambers of the left hydraulic cylinder
and the right hydraulic cylinder are made to communicate with each
other via a restrictor, the head chambers of the left and right
hydraulic cylinders are also connected to an accumulator via a
pressure control valve. The line between the pressure control valve
and the accumulator is connected to a hydraulic pump via a check
valve which allows hydraulic oil to flow toward the accumulator. As
a result, while the body moves vertically due to the contraction of
the hydraulic cylinders when the wheels are subject to strong
impact during travelling, the load is damped since the pressure
control valve opens to communicate the hydraulic cylinders to the
accumulator. If either of the left wheel or the right wheel is
subject to an impact, the pressure oil from one of the hydraulic
cylinders flows into the other hydraulic cylinder to rock the
body.
[0014] In the work vehicle disclosed in Japanese Laid-Open Patent
Publication No. H 6-278438 or Japanese Laid-Open Patent Publication
No. H 7-132723 (hereafter referred to as prior art 2),
double-acting hydraulic cylinders are mounted at the right side
surface and the left side surface of the body with head chambers of
the hydraulic cylinders connected with each other via a piping. A
restrictor and an accumulator are provided in the middle of the
piping and the lower ends of the cylinder rods of the hydraulic
cylinders are individually linked to the axle of the work vehicle
with pins. Thus, the vibration of the axle occurring during
travelling is absorbed and damped to improve the comfort of the
operator while travelling the vehicle.
[0015] Japanese Laid-Open Patent Publication No. H 7-125523
discloses a work vehicle (hereafter referred to as prior art 3)
achieved by linking the upper ends of the cylinder tubes of one set
of hydraulic cylinders and the lower ends of the cylinder rods
respectively to the center of the body and the center of the axle
with pins and linking the center of the axle and either the left
side or the right side of the body with a link. In this vehicle,
the bottom chamber of the hydraulic cylinder is connected to an
accumulator via a restrictor. As a result, while the body moves in
the vertical direction due to the contraction of the hydraulic
cylinders if the wheels are subject to a strong impact during
travelling, the load on the hydraulic cylinder communicating with
the accumulator is attenuated.
SUMMARY OF THE INVENTION
[0016] The work vehicles disclosed in the publications above
present the following problems. Namely, in the work-vehicle in
prior art 1 having the body and the axle linked with each other
through a pin, a load applied to the body and the axle along the
forward/backward direction during an excavating operation or due to
brakes applied on the travelling vehicle must be borne by the pin
and, therefore, it is necessary to use a large pin having a large
pin diameter to assure a sufficient degree of pin strength. In
addition, the pin used to restrict the movement of the axle
relative to the body slides along the vertical direction as the
axle moves up and down, hastening the process in which the sliding
area becomes worn. As a result, the play of the pin in the long
hole increases, which causes a displacement of the axle relative to
the body along the horizontal direction as well as along the
vertical direction, thereby making it difficult to smoothly absorb
an impact. Furthermore, since single-acting hydraulic cylinders are
utilized, which are engaged only when they contract, an impact
cannot be hydraulically absorbed while they are extended, allowing
the impact to be applied to the component members.
[0017] Since the body and the axle are linked to each other by the
left hydraulic cylinder and the right hydraulic cylinder in the
work vehicle in prior art 2, an excessive load is applied to the
hydraulic cylinders in the forward/backward direction and the
lateral direction as well as along the vertical direction while the
vehicle is engaged in an excavating operation or if the vehicle is
rocked.
[0018] In the work vehicle in prior art 3, since the body and the
axle are linked to each other through the central hydraulic
cylinder and the link, there is no means for limiting the rocking
movement of the body, and thus, a shock related to the rocking
movement cannot be absorbed. Thus, the work vehicle disclosed in
the publication, in which the frame is not allowed to move
vertically or to rock in a smooth manner while absorbing any impact
from the axle, is not suited for practical use.
[0019] The work vehicles in prior art 2 and prior art 3 also
present a problem in that while a fixed restrictor is provided in
the passage between the hydraulic cylinder and the accumulator, the
bottom chamber and the rod chamber of the hydraulic cylinder are
not made to communicate with each other, which allows the
attenuating force of the suspension to entirely depend upon the
size of the sectional area of the variable constriction, thereby
presenting difficulty in satisfying the personal preferences of
individual operators.
[0020] Furthermore, since the movement of the left hydraulic
cylinder and the right hydraulic cylinder are adjusted by a single
accumulator in the work vehicles in prior art 1 through prior art
3, the capacity of the accumulator is bound to be large, which
necessitates the scale of the accumulator to be large as well. It
is difficult to fit such a large accumulator within the limited
space inside the body through efficient space utilization, which
places limits on the degree of flexibility with regard to wheeled
hydraulic excavator design. In particular, if a bladder-type
hydro-pneumatic accumulator is to be utilized, its structure
necessitates that it be installed vertically, placing further
restrictions on the installation arrangement. As a result, the
accumulator may need to be installed with a part thereof projecting
out from the body and, in such a case, a falling object or the like
may collide with the projecting portion to damage the
accumulator.
[0021] The work vehicle in prior art 2 is provided with a
spool-type three ports/three positions solenoid control valve for
leveling the height of the vehicle. By switching this solenoid
control valve, the pressures in the hydraulic cylinders are
controlled so as to set the distance between the axle and the body
while the vehicle travels or it is engaged in operation to a
predetermined specific value, to level the height of the
vehicle.
[0022] However, since the suspension performance is effected while
controlling the pressure at the hydraulic cylinder while the
vehicle travels, it is difficult to correctly set the various parts
(such as the restrictor) that affect the suspension performance in
the work vehicle in prior art 2. In addition, since the pressures
at the hydraulic cylinders are controlled during operation as well,
the suspension is soft, which may cause the operator some
discomfort.
[0023] Furthermore, a spool-type solenoid control valve is utilized
in the work vehicle in prior art 2, and the solenoid control valve
is switched to the neutral position to cut off the hydraulic
cylinders from the hydraulic source or the tank when it is riot
necessary to level the height of the vehicle such as when the
vehicle travels. However, since spool-type control valves tend to
readily allow leaks at the neutral position, there is a concern
that the vehicle height may change while the vehicle travels or
while it is in a stationary state.
[0024] The vehicle height is leveled primarily to sustain a
specific standard vehicle attitude when the weight balance between
the front and the rear of the vehicle changes (e.g., the body leans
forward) due to a front attachment replacement. Accordingly, the
vehicle should be leveled through an operation performed outside
the cabin while visually checking any change occurring in the
vehicle attitude and, as a result, the height of vehicle cannot be
fine-tuned through an operation performed within the cabin with
ease.
[0025] However, if an operating lever to be used to operate a
leveling control valve is provided outside the cabin in order to
achieve leveling through an operation of the operating lever, the
operating lever may be inadvertently turned due to an impact from
the road surface even when the vehicle is not being leveled such as
while it is travelling, to accidentally switch the control valve to
a position other than the neutral position. This will result in an
undesirable fluctuation in the vehicle height.
[0026] Moreover, if the operating lever to be used to operate the
leveling control valve is provided outside the cabin, the
operability is compromised and the operating lever may even be
damaged by an object falling from the front. In addition, when the
suspension circuit is formed by switching the leveling control
valve to the neutral position, it is necessary to take into
consideration the positional relationship between the control valve
and the accumulator in order to obtain the maximum suspension
performance (in particular, the maximum accumulator performance)
since the distance from the control valve to the accumulator
affects the suspension performance.
[0027] An object of the present invention is to provide a wheeled
work vehicle capable of effectively absorbing an impact occurring
while the vehicle is travelling.
[0028] In order to achieve the object described above, the wheeled
work vehicle according to the present invention comprises a link
that links at least one of axles provided at the front and the rear
of the vehicle to the chassis, suspension hydraulic cylinders
provided on the left and right sides of the chassis, which connect
the axle to the chassis in conjunction with the link and an
accumulator that is allowed to communicate with the oil chambers of
the hydraulic cylinders via restrictors.
[0029] This structure allows the axle to smoothly move along the
vertical direction and also to smoothly rock relative to the frame
to enable efficient absorption of a shock occurring when the
hydraulic cylinders expand/contract, to facilitate the adoption of
the work vehicle in practical use.
[0030] The work vehicle according to the present invention may
further comprise a means for adjustment that changes the suspension
performance in correspondence to the area of the passages
communicating between the bottom chambers and the rod chambers of
the hydraulic cylinders. By providing such a means for adjustment,
the suspension performance, in particular the damping performance
can be changed with ease.
[0031] The work vehicle may further comprise a means for adjustment
that changes the suspension performance in correspondence to the
area of the passages communicating between the hydraulic cylinders
and the accumulator. By providing such a means for adjustment, the
suspension performance and, in particular, the damping performance
can be adjusted with ease.
[0032] It is desirable to use a diaphragm-type accumulator that
separates the internal gas and the oil through a diaphragm and to
install the accumulator in the space formed by the frame without
any parts of the accumulator projecting out from the upper end
surface and the lower end surface of the chassis. The accumulator
thus installed within the limited space with a high degree of
efficiency is protected from falling objects and the like.
[0033] The wheeled work vehicle according to the present invention
may comprise a hydraulic source from which pressure oil originates,
a supply/discharge device that expands/contracts the hydraulic
cylinders by supplying the pressure oil to the hydraulic cylinders
and discharging the pressure oil from the hydraulic cylinders, a
traveling-state detection device that detects whether the vehicle
is in a travelling state or in a non-travelling state and a
leveling/suspension switching device that allows the
supply/discharge device to expand/contract the hydraulic cylinders
when the traveling-state detection device detects that the vehicle
is in a non-travelling state and prohibits the
expansion/contraction of the hydraulic cylinders by the
supply/discharge device if the traveling-state detection device
detects that the vehicle is in a travelling state to engage a
suspension function.
[0034] This eliminates the necessity for taking into consideration
the requirements that must be met to realize a leveling function
when designing the suspension performance to be achieved while the
vehicle travels, to facilitate settings to be made at the various
components involved in achieving the suspension performance.
[0035] Alternatively, it is desirable that the wheeled work vehicle
according to the present invention further comprise a hydraulic
source from which pressure oil originates and a leveling valve that
switches the oil supply/discharge path to/from the hydraulic
cylinders during a leveling operation in response to an operation
of an operating lever, with the operating lever projecting out from
a side surface of the chassis further toward the front of the
vehicle relative to the axle.
[0036] This improves the operability during a leveling operation
since the operator does not need to insert his hand into the
recessed part so as to operate the operating lever, and also it
allows the operator to visually check for any positional changes
occurring with regard to the positions of the hydraulic cylinders
and the link connecting the body to the axle to enable a highly
reliable leveling operation to be performed with ease.
[0037] As a further alternative, the wheeled work vehicle according
to the present invention may further comprise a hydraulic source
from which pressure oil originates, a leveling valve that switches
the oil supply/discharge path to/from the hydraulic cylinders
during a leveling operation and a stop valve that disconnects the
supply/discharge path from the hydraulic cylinders.
[0038] By adopting the structure described above, the quantity of
oil that is leaked from the hydraulic cylinder is minimized, to
prevent the upper swiveling body from being lowered to an
undesirable extent.
[0039] It may be further provided with a retaining member that is
utilized to operate the stop valve at the travelling body and to
retain the stop valve at the cutoff position. Such a retaining
member retains the stop valve at the cutoff position even if an
external impact is applied when the stop valve is switched to the
cutoff position to minimize the leak from the hydraulic cylinders
reliably.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 is a side elevation of a wheeled hydraulic excavator
adopting the present invention;
[0041] FIG. 2 is a bottom view of the wheeled hydraulic excavator
adopting the present invention (from the direction indicated by the
arrow at II in FIG. 1);
[0042] FIG. 3 is a front view of the wheeled hydraulic excavator
adopting the present invention;
[0043] FIG. 4 is a sectional view taken along line IV-IV in FIG.
2;
[0044] FIG. 5 is a sectional view taken along line V-V in FIG.
2;
[0045] FIG. 6 presents a view from the direction indicated by the
arrow at VI n FIG. 5;
[0046] FIG. 7 presents a view from the direction indicated by the
arrow at VII in FIG. 5;
[0047] FIG. 8 is an enlargement of area VIII in FIG. 2;
[0048] FIG. 9 is an enlargement of area IX in FIG. 3;
[0049] FIG. 10 is a view from the direction indicated by the arrow
at X in FIG. 8;
[0050] FIG. 11 is a hydraulic circuit diagram of the wheeled work
vehicle achieved in the first embodiment of the present
invention;
[0051] FIG. 12 is a sectional view of the ball-type three-position
switching valve constituting hydraulic circuit of the wheeled work
vehicle in the first embodiment of the present invention;
[0052] FIG. 13 is a sectional view of a block internally provided
with the pilot check valves included in conjunction with a
hydraulic cylinder constituting the hydraulic circuit of the
wheeled work vehicle in the first embodiment of the present
invention;
[0053] FIG. 14 is an electric circuit diagram of the-wheeled work
vehicle achieved in the first embodiment of the present
invention;
[0054] FIGS. 15A and 15B present an example of the suspension
operation achieved in the wheeled work vehicle in the first
embodiment of the present invention;
[0055] FIGS. 16A, 16B and 16C show the expanded/contracted states
of a hydraulic cylinder in the wheeled work vehicle in the first
embodiment of the present invention;
[0056] FIG. 17 presents an example of a variation of FIG. 6;
[0057] FIG. 18 is a hydraulic circuit diagram of the wheeled work
vehicle achieved in the second embodiment of the present
invention;
[0058] FIG. 19 is a flow chart of an example of the processing
executed by the controller of the wheeled work vehicle in the
second embodiment of the present invention;
[0059] FIG. 20 presents another example of how the sectional size
of the passage communicating between the bottom chamber and the rod
chamber of a hydraulic cylinder constituting the hydraulic circuit
of the wheeled work vehicle in the embodiment of the present
invention may be varied;
[0060] FIGS. 21A and 21B show other methods that may be adopted to
retain the position of the leveling switching lever in the wheeled
work vehicle achieved in the embodiment of the present
invention;
[0061] FIG. 22 is another example of a hydraulic circuit diagram of
the wheeled work vehicle of the present invention; and
[0062] FIG. 23 is another example of an electric circuit diagram of
the wheeled work vehicle of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0063] the following is an explanation of preferred embodiments of
the present invention, given in reference to the drawings.
[0064] -First Embodiment-
[0065] FIG. 1 is a side elevation (a partial sectional view) of a
wheeled hydraulic excavator in which the present invention is
adopted. As illustrated in FIG. 1, the wheeled hydraulic excavator
includes a lower travelling body 81 and an upper swiveling body 83
which is rotatably linked to the top of the lower travelling body
81 via a swiveling device 82. At the upper swiveling body 83, a
front attachment 84 (hereafter referred to as an attachment)
constituted of a boom 84A, an arm 84B and a bucket 84C and an
operator's cab 85 are provided, with a gate lock lever 86 which is
operated to a release position (position A) when the operator
boards the vehicle and is operated to a locked position (position
B) when the operator leaves the vehicle provided at the entrance of
the operator's cab 85. A chassis frame 70 (hereafter referred to as
a frame), a travelling hydraulic motor 88, a transmission 89, a
propeller shaft 90 and tires 91 are provided at the lower
travelling body 81, and the drive force imparted from the propeller
shaft 90 is communicated to the tires 91 via axles 1 and 1'.
Fenders 61F and 61R are provided to cover the tops of the tires 91
at the front and the rear of the frame 70, and hydraulic cylinders
2 which are to be detailed later are provided inside the front
fender 61F. It is to be noted that the frame 70 includes a bucket
stage 87 provided at its front-most end. In this embodiment, the
rear axle 1' is directly secured to the frame 70, whereas the front
axle 1 is linked to the frame 70 via the suspension mechanism
described below.
[0066] FIG. 2 is a bottom view of the wheeled hydraulic excavator
adopting the present invention (viewed from the direction indicated
by the arrow II in FIG. 1), FIG. 3 shows the lower travelling body
81 viewed from the front of the vehicle (a front view of FIG. 1),
FIG. 4 is a sectional view taken along line IV-IV in FIG. 2
primarily illustrating how of the accumulator 7 is mounted and FIG.
5 is a sectional view taken along line V-V in FIG. 2 primarily
illustrating how the hydraulic cylinders 2 are mounted. It is to be
noted that in FIGS. 2.about.5, the body is in a stationary state
(initial state). In addition, the illustration of the axle 1, which
is located directly under the hydraulic cylinders 2, is omitted in
FIG. 2, and the frame 70 and the axle 1 are indicated by the
two-point chain lines in FIG. 5. As shown in FIGS. 2.about.5, the
frame 70 includes right and left side plates 71 and 72 provided at
the front of the vehicle, a front plate 73 and a rear plate 74
respectively in contact with the front end surfaces and the rear
end surfaces of the side plates 71 and 72, right and left side
plates 75 and 76 (each having a roughly U-shaped cross section, as
shown in FIG. 4) that are in contact with the rear plate 74 and are
provided at the rear of the vehicle and an upper plate 77 which is
in contact with the upper surfaces of the individual plates
71.about.76. The right and left ends of the front plate 73 extend
further but compared to the side plates 71 and 72, and the fender
61F is mounted at extending portions. 73s (see FIGS. 2 and 3).
[0067] FIG. 6 presents a view taken along the direction indicated
by the arrow VI in FIG. 5, and FIG. 7 presents a view (an
enlargement of the essential portion in FIG. 2), taken along the
direction indicated by the arrow VII in FIG. 5. It is to be noted
that the frame 70 and the axle 1 are indicated by the two-point
chain lines in FIGS. 6 and 7. As illustrated in FIGS. 5.about.7, a
pair of brackets 3 is fastened with bolts 51 to each of the side
plates on the front side, i.e. the right and left side plates 71
and 72 with the brackets 3 in a pair provided over distance from
each other along the forward/backward direction. A circular opening
3a is formed at the upper portion of each bracket 3. Projections 2t
provided at the front and rear of the upper side surface of the
cylinder tube of the hydraulic cylinder 2 are fitted inside the
openings 3a, so as to rotatably support the cylinder tube. The
positions at which the brackets 3 are mounted at the side plates 71
and 72 are set with knock pins 52 to prevent the projections 2t of
the hydraulic cylinders 2 from one-sidedly coming in contact with
the inner surfaces of the openings 3a at the brackets 3. It is to
be noted that the method whereby the hydraulic cylinders 2 are
clamped with a pair of brackets 3 in this manner is referred to as
a trunnion method. The ends of piston rods 2a are rotatably linked
to the axle 1 via pins 92. In this structure, the pair of hydraulic
cylinders 2 provided at the left and the right sides are mounted by
ensuring that axes 2L of the hydraulic cylinders 2 form a
substantially "A-line shape" (Japanese character""shape), i.e., so
that the ends of the piston rods 2a turn outward along the width of
the vehicle, in the initial state.
[0068] As illustrated in FIGS. 5 and 7, the front plates 73 and the
rear plate 74 are connected to the center of the axle 1 (on the
center line 1L) at either the left side or the right side (at the
left side in the figures) by a link 4 which is provided through an
opening at the bottom of the frame 70. The link 4, which is
constituted of main plates 4a provided at the front and the rear
over a distance from each other, reinforcement plates 4b each
welded to the outer surface of a main plate 4a toward the axle,
three side plates 4c.about.4e each having the two ends thereof
welded to the inner surfaces of the main plates 4a and pipe 4f
welded to the outer surfaces of the main plates 4a toward the body
frame 70, forms a box-shaped closed space with its side plates
4c.about.4e and pipe 4f. Inner plates 73a and 74a are provided over
a distance equal to the axial length of the pipe 4f from each
other, respectively at the front plate 73 and the rear plate 74 of
the frame 70, and by fitting the pipe 4f between the inner plates
and inserting a pin 93 in the pipe 4f, the frame 70 and the link 4
are rotatably linked with each other via the pin 93. In addition, a
mounting member 1a used to mount the link 4 is. provided on the
axle 1, and by setting the main plates 4a so as to clamp the
mounting member 1a between them and inserting a pin 94, the axle 1
and the link 4 are rotatably linked with each other via the pin
94.
[0069] By individually connecting the frame 70 to the link 4 and
the axle 1 to the link 4 with the pins as described above, the link
4 is allowed to rotate by using the pin 93 as a support point as
indicated by the arrow in FIG. 3 and the axle 1 is allowed to move
mainly vertically relative to the frame 70 within the
expansion/contraction range of the piston rods 2a, as shown in FIG.
3. In addition, the axle 1 may engage in a rocking movement with
the pin 94 constituting the support point within the range of the
expansion/contraction of the piston rods 2a under certain
circumstances. The mounting tolerance for the link 4 should be set
as rigorously as possible in order to ensure that the fitting
tolerance with regard to the axial length of the pipe 4f and the
distance between the pair of inner plates 73a and 74a of the frame
70 (the clearance at the fitting area L1 in FIG. 7) and the fitting
tolerance with regard to the distance between the pair of main
plates 4a and the axial length of the mounting member 1a of the
axle 1 (the clearance at the fitting area L2 in FIG. 7). are
smaller than the play manifesting at the areas where the hydraulic
cylinders 2 are mounted. By enforcing such a rigorous setting, it
becomes possible to allow the load from the frame 70 applied along
the frontward/backward direction of the body to be communicated to
the axle 1 via the link 4 instead of via the hydraulic cylinders
2.
[0070] As illustrated in FIG. 3, a notched portion 73c having
projections 73b on the inside thereof is provided at the bottom
center of the front plate 73 to allow the top of the pin 94 to be
seen from the front of the vehicle. A nipple 94a for grease
injection is provided at the center of the head of the pin 94, and
the height of the vehicle is adjusted as described later while
visually checking the positional relationship between the nipple
94a and the projections 73b at the front plate 73 (the relationship
between their heights).
[0071] Next, the arrangement of the hydraulic pipings is explained.
As shown in FIG. 2, the right and left hydraulic cylinders 2 are
connected with each other via a line 5, with the accumulator 7
connected in the middle (at the center) of the line 5 via a line 6.
The accumulator 7 is also connected with a directional control
valve 8 whose position is switched through a manual operation of a
switching lever 8a via a piping 9, and the directional control
valve 8 is connected to a center joint 11 via a piping 10. A
detailed explanation of the hydraulic circuit is to be given later
in reference to FIG. 11. It is to be noted that a hydraulic pump 13
and a tank which are to be explained later are mounted at the upper
swiveling body 83 (see FIG. 1), and during a leveling operation,
the pressure oil from the hydraulic pump 13 is supplied to the
hydraulic cylinders 2, the accumulator 7 and the like provided at
the lower travelling body 81 via the center joint, 11 and the oil
from the hydraulic cylinders 2 is discharged into the tank via the
directional control valve 8 and the center joint 11.
[0072] The accumulator 7 is a so-called diaphragm-type accumulator
7 that separates the internal gas from the oil through a diaphragm,
and has the substantially following features in comparison to a
so-called bladder-type hydro-pneumatic accumulator which separates
the internal gas from the oil through a bladder. Namely, the
overall shape of the diaphragm-type accumulator is round with a
smaller height along the lengthwise direction compared to that of
the bladder-type hydro-pneumatic accumulator. In addition, the
structure of the diaphragm-type accumulator does not impose any
restrictions on the attitude, which allows the accumulator to be
positioned by setting its length along the vertical direction
(hereafter referred to as a vertical installation) or to be
positioned by setting its length along the horizontal direction
(hereafter referred to as a horizontal installation). Due to its
structural restrictions, the bladder-type hydro-pneumatic
accumulator cannot be installed horizontally with ease. As shown in
FIG. 4, the diaphragm-type accumulator 7 is installed along the
horizontal direction in the embodiment.
[0073] As illustrated in FIG. 4, the right and left side plates 75
and 76 at the rear of the frame 70 have a roughly U-shaped cross
section, thereby creating laterally elongated. spaces between the
upper plate 77 and the side plates 75 and 76. A bracket 77a having
an L-shaped cross section is welded onto the lower surface of the
upper plate 77 (see FIG. 2), and a leg member 40a formed as an
integrated part of a band 40 is fastened onto the bracket 77a with
bolts 41. The band 40 is formed to achieve a roughly C shape and
the accumulator 7 is mounted inside the band 40. A bolt 42 is
inserted at the two ends of the band 40, and a nut 43 is screwed on
the bolt 42 so that the band 40 is caused to contract by tightening
the bolt 42 to secure the accumulator 7. It is to be noted that the
line 5 mentioned earlier is suspended from the left and right side
plates 75 and 76 via piping retaining members 44.
[0074] The accumulator 7 is installed in the space formed between
the left and right side plates 75 and 76 by ensuring that its upper
end does not project-out further above the upper plate 77 and that
its lower end does not project out further below the lower end
surfaces of the side plates 75 and 76. In other words, the entire
accumulator 7 is contained within the space defined by the upper
end surface and the lower end surface of the frame 70. By
installing the accumulator 7 in this manner, the accumulator 7 is
completely housed inside the frame 70, to be protected from falling
objects and the like and also to improve the visual aspect of the
design. In addition, since the accumulator 7 is horizontally
installed, the line 6 connected to the accumulator 7 does not
project out downward. It is to be noted that while the line 5
connecting the left and right hydraulic cylinders 2 with each other
is allowed to project out below the lowermost surfaces of the side
plates 75 and 76 to extend laterally so as to be suspended from the
side plates 75 and 76, the extent to which the line 5 projects out
further below the side plates 75 and 76 can be minimized since
there is no distended portion attributable to the line 6. If a
bladder-type hydro-pneumatic accumulator is to be installed instead
of the diaphragm-type accumulator 7 utilized in the embodiment, it
becomes difficult to house the accumulator within the space formed
by the left and right side plates, 75 and 76 and the upper plate 77
because of its greater height.
[0075] Now, the mounting position of the switching lever 8a
operated to switch the directional control valve 8 is explained.
FIG. 8 is an enlarged view of area VIII (a partial sectional view)
in FIG. 2. and FIG. 9 is an enlarged view of area IX (a partial
sectional view) in FIG. 3. As shown in FIGS. 8 and 9, a slot 71a
extending along the vertical direction is provided at a part of the
side plate 71 which is set further frontward of the vehicle
relative to the hydraulic cylinders 2, and the switching lever 8a
passes through the slot 71a to project to the outside of the side
plate 71. When viewed from the front of the vehicle, the entire
switching lever 8a is hidden by the fender 61F, with the fender 61F
covering the switching lever 8a from the above relative to the
vehicle. The switching lever 8a can be operated along the slot 71a,
and if the switching lever 8a is set to a position A from the
neutral position shown in FIG. 9, the directional control valve 8
is switched as detailed later to raise the height of the vehicle,
whereas if it is set to a position B, the directional control valve
8 is switched as described later to lower the height of the
vehicle.
[0076] FIG. 10 presents a view of FIG. 8 taken from the right (a
view taken from the direction indicated by the arrow X in FIG. 8).
A retaining cover 45 is provided as in order to prevent the
switching lever 8a from being inadvertently switched when, for
instance, the switching lever 8a is subjected to an impact of a
falling object coming from the right, vibration or the like, as
shown in FIGS. 8.about.10. The retaining cover 45 is constituted of
a roughly rectangular thin plate that covers the slot 71a and is
secured to the side plate 71 with two wing nuts 46. A notched
portion 45a is formed at a part (at a position corresponding to the
neutral position of the switching lever 8a) of the retaining cover
45, and this notched portion 45a restricts the movement of the
switching lever 8a when the vehicle is not being leveled. During
the leveling operation, the wing nuts 46 are loosened to remove the
retaining cover 45 and thus, the movement of the switching lever 8a
becomes unrestricted.
[0077] FIG. 11 is a hydraulic circuit diagram illustrating the
structure adopted in the suspension of the wheeled work vehicle in
the first embodiment of the present invention. The suspension in
the embodiment achieves a leveling function and a suspension lock
function in addition to a suspension function effected when the
vehicle travels. As shown in FIG. 11, the accumulator 7 is
connected to the main hydraulic source 13 via the directional
control valve 8, the center joint 11 and a hydraulic pilot
controlled directional control valve 12. A pilot port 12a of the
hydraulic pilot controlled directional control valve 12 is
connected to a pilot hydraulic source 16 via a solenoid controlled
directional control valve 14 and a lock valve 15. The position of
the lock valve 15 is switched through an operation of the gate lock
lever 86 provided at the operator's cab 85. Namely, when the gate
lock lever 86 is set to the release position, the lock valve is
switched to position (a), whereas if the gate lock lever 86 is set
to the lock position, the lock valve 15 is switched to position
(b). The solenoid controlled directional control valve 14 is
switched to position (b) when its solenoid 14a is excited in
response to an electrical signal I to be detailed later and is
switched to position (a) as its solenoid 14a becomes
demagnetized.
[0078] When the lock valve 15 and the solenoid controlled
directional control valve 14 are both switched to position (b),
pilot pressure from the pilot hydraulic source 16 is supplied to
the pilot port 12a of the hydraulic pilot controlled directional
control valve 12 and, as a result, the hydraulic pilot controlled
directional control valve 12 is switched to position (b). This
allows the pressure oil from the main hydraulic source 13 to be
supplied to the directional control valve 8, to enable an
adjustment operation for raising the vehicle height. If, on the
other hand, at least either the lock valve 15 or the solenoid
controlled directional control valve 14 is switched to position
(a), the pilot port 12a of the hydraulic pilot controlled
directional control valve 12 becomes communicated with the tank,
thereby switching the hydraulic pilot controlled directional
control valve 12 to position (a). Thus, the directional control
valve 8 becomes communicated with the tank to prohibit the
adjustment operation for raising the vehicle height, thereby
enabling an adjustment operation to lower the vehicle height.
[0079] The directional control valve 8 is a three-port
/three-position switching valve which may be constituted of, for
instance, a ball valve as shown in FIG. 12. The directional control
valve 8 is switched to position (a) in FIG. 11 when the switching
lever 8a is set to position A in FIG. 9 to allow an A port 8A to
communicate with a P port 8P. If, the other hand, the switching
lever 8a is set to position B in FIG. 9, the directional control
valve 8 is switched to position (c) to allow the A port 8A to
communicate with a T port 8T. When the switching lever 8a is set to
the neutral position, the directional control valve 8 is switched
to position (b) and, as a result, the A port 8A becomes completely
cut off from the P port 8P or the T port 8T, as illustrated in FIG.
12 to keep down the quantity of oil leaked from the A port 8A at
near 0 level.
[0080] The directional control valve 8 is constituted of a body 8b
at which the P port (pump port) 8P, the T port (tank port 8T and
the A port (service port) 8A are provided and a ball 8c provided
inside the body 8b which can be set to position (a), position (b)
or position (c) through an external operation. Thus, the
directional control valve 8 functions both as a directional control
valve that switches the flow of the pressure oil and as a stop
valve used to ensure that the quantity of oil leak is sustained at
a near 0 level by blocking the pressure oil flow. When the ball 8c
is operated between position (a) and position (b), an opening area
corresponding to the degree to which the ball 8c is moved is
achieved, thereby enabling the directional control valve 8 to
function as a stop valve with a so-called metering capability.
[0081] As illustrated in FIG. 11, a restrictor 6a with an area A1
is provided at the line 6 connected to the accumulator 7 and
restrictors 5a with an area A2 are provided at the line 5
communicating between a pair of cylinder blocks 3, with the
restrictors 5a and 6a achieving a relationship expressed as
A1>A2. As high-pressure oil is supplied into the line 5 in
response to a contraction of the hydraulic cylinders 2, the
pressure from the pressure oil is accumulated at the accumulator 7
via the restrictors 5a and 6a, and the pressure oil with its
pressure thus built up is supplied to the individual hydraulic
cylinders 2 to reset the vehicle to the neutral position. In this
situation, the accumulator 7 functions as a spring that mainly
absorbs vibration, whereas the variable constrictions 5a and 6a
constituting resistors function, as a damper that mainly damps the
vibration. The characteristics of the spring and the damper are
determined in correspondence to the pressure of the gas charged
into the accumulator 7 and the areas of the restrictors 5a and
6a.
[0082] The line 5 is branched to extend in two directions inside
each cylinder block 3, with one branch (a passage C2 in FIG. 13)
connected to the head chamber 2b of the hydraulic cylinder 2 via a
pilot check valve 17 and the other branch (a passage C1 in FIG. 13)
connected to the rod chamber 2c of the hydraulic cylinder 2 via a
restrictor 5b having an area A3 (the area A3, which is smaller than
the area A1, is variable as detailed later) and a pilot check valve
17. The pilot ports of the pilot check valves 17 are connected to
the pilot hydraulic source 16 via an solenoid controlled
directional control valve 18, and the drive of the pilot check
valves 17 is controlled by switching the solenoid controlled
directional control valve 18. The solenoid controlled directional
control valve 18 is switched to position (b) as its solenoid 18a
becomes excited by the electrical signal I to be detailed later and
is switched to position (a) as the solenoid 18a becomes
demagnetized.
[0083] When the solenoid controlled directional control valve 18 is
switched to position (b), the pressure oil from the pilot hydraulic
source 16 is supplied to the pilot ports of the pilot check valves
17. Thus, the pilot check valves 17 function simply as release
valves to allow the pressure oil to flow from the oil chambers 2b
and 2c of the hydraulic cylinders 2 (an unlocked state). It is to
be noted that the flow of the pressure oil at the head chambers 2b
and the rod chambers 2c is regulated by the restrictors 5b in this
situation, i.e., the restrictors 5b function as a damper that
mainly damps vibration. When the solenoid controlled directional
control valve 18 is switched to position (a), the supply of the
pressure oil from the pilot hydraulic source 16 is stopped, thereby
allowing the pilot check valves 17 to function as normal check
valves and, as a result, any movement of the pressure oil from the
oil chambers 2b and 2c at each hydraulic cylinder 2 becomes
prohibited (a locked state).
[0084] A wheeled hydraulic excavator is normally engaged in an
excavating operation with the front attachment 84 turned toward the
rear of the vehicle and thus, the vehicle often travels by leaving
the front attachment 84 turned rearward at the work side. Since
this shifts the center of gravity of the body toward the rear axle
1', which would allow the rods 2a to expand under normal
circumstances, the oil flowing out from the rods 2a would directly
flow into the head chambers 2b to cause the rods 2a to extend to
the stroke limit, and the comfort of the operator would be
compromised by the impact occurring at the limit of the stroke
unless the restrictors 5b were provided at the communicating
passages between the rod chambers 2c and the head chambers 2b.
Accordingly, the restrictors 5b are provided to achieve a
pseudo-spring effect to realize firm suspension performance. In
this structure, the restrictors 5b can also be utilized to adjust
the degree of firmness to a suitable value with ease.
[0085] FIG. 13 shows an example in which the pilot check valves 17
and the restrictor 5b are internally provided at an integrated
block IB which is then mounted at each suspension hydraulic
cylinder 2 as an integrated cylinder. It is to be noted that in
FIG. 13, the pair of pilot check valves are referred to as 17A and
17B. The block IB includes five external ports, i.e., a bottom
chamber port P1, a rod chamber port P2, an accumulator port P3, a
pilot port P4 and a drain port P5. The pilot check valves 17A and
17B are each constituted of a movable valve element 17a, a spring
17b that applies a force to the movable valve element 17a, a
plunger 17c that drives the movable valve element 17a and a return
spring 17d of the plunger 17c. Chambers 17e of the pair of pilot
check valves 17A and 17B are made to communicate with each other
through the passage C1 at which a variable restrictor VD is
provided, and the passage C1 communicates with the accumulator port
P3 through the passage C2. The damping performance of the
suspension is adjusted by varying a restrictor area of the variable
restrictor VD through an external operation. Chambers 17f of the
pair of pilot check valves 17A and 177B are made to communicate
with the pilot port P4 and drainage chambers 17g of the pair of
pilot check valves 17A and 17B are made to communicate with the
drain port P5.
[0086] In a travelling mode, the plungers 17c move to the right as
the pilot pressure is applied to the pilot port P4 to push the
movable valve elements 17a, thereby allowing the pilot check valves
17A and 17B to function as release valves and ultimately allowing
the hydraulic cylinder 2 to function as a suspension. The pilot
pressure is not applied to the pilot port P4 in a parking mode or
in working mode. In parking mode or working mode, the movable valve
elements 17a are not pushed to the right and thus, the pilot check
valves 17A and 17B are able to function as check valves through the
force applied by the spring 17b, thereby cutting off the head
chamber 2b and the rod chamber 2c of the suspension hydraulic
cylinder 2 from the accumulator port P4 and setting the suspension
hydraulic cylinder 2 in a locked state.
[0087] FIG. 14 is an electric circuit diagram of the suspension in
the wheeled work vehicle achieved in the first embodiment. As shown
in FIG. 14, a relay circuit is constituted with a brake switch 21
which is a switched to a T contact point 21T, a P contact point 21P
or a W contact point 21W in correspondence to the mode setting,
i.e. the travelling mode, the parking mode or the working mode, a
leveling switch 22 that issues an instruction for leveling the
height of the vehicle in response to an operation performed at the
operator's cab 85, a power source 23 and relays 24, 25 and 26 in
the electric circuit, and this relay circuit implements control on
whether or not the electrical signal I is to be provided to the
solenoids 14a and 18a of the solenoid controlled directional
control valves 14 and 18, a solenoid 27 for parking brake release
and a solenoid 28 for working brake activation.
[0088] To give a more detailed explanation in reference to FIG. 14,
a common contact point 21s of the brake switch. 21 is connected to
the power source 23, the T contact point 21T is connected to an "a"
contact point 24a of the relay 24, a coil 25c of the relay 25 and
the solenoid 27 for parking brake release and the W contact point
21W is connected to a coil 26c of the relay 26 and the solenoid 28
for working brake activation, with the P contact point 21P left
open. As the brake switch 21 is switched to the W contact point
21W, the solenoid 28 for working brake activation becomes excited
to engage the working brake and, at the same time, the solenoid 27
for parking brake release becomes demagnetized to engage the
parking brake as, well. When the brake switch 21 is switched to the
P contact point 21P, the solenoid 27 for parking brake release
becomes demagnetized to engage the parking brake. It is to be noted
that the illustration of the working brake and the parking brake
which are of the known art is omitted.
[0089] The solenoid 18a of the solenoid controlled directional
control valve 18 is connected to a common contact point 24s of the
relay 24, a "b" contact point 24b of the relay 24 is connected to
an "a" contact point 26a of the relay 26, a common contact point
26s of the relay 26 is connected to the power source 23 and a "b"
contact point 26b of the relay 26 is left open. In addition, a
solenoid 14a of the solenoid controlled directional control valve
14 is connected to the leveling switch 22, the leveling switch 22
is connected to an "a" contact point 25a of the relay 25 and a
common contact point 25s of the relay 25 is connected to the power
source 23, with a "b" contact point 25b of the relay 25 left open.
As a result, when the brake switch 21 is switched to the P contact
point 21P or to the W contact point 21 W, the relay 25 is switched
to the "a" contact point 25a, and if the leveling switch 22 is
turned on in this state, the solenoid 14a of the solenoid
controlled directional control valve 14 becomes connected to the
power source 23 and thus becomes excited. If, on the other hand,
the brake switch 21 is switched to the P contact point 21P and the
leveling switch 22 is turned on, the relay 24 and the relay 26 are
respectively switched to the "b" contact point 24b and the "a"
contact point 26a and, as a result, the solenoid 18a of the
solenoid controlled directional control valve 18 becomes connected
to the power source 23 and thus becomes excited. In other words, by
turning on the leveling switch 22 in the parking mode, the pilot
check valves 17 are set in a released state to enable a leveling
operation through an operation of the switching lever 8a as long as
other leveling conditions are met. If the brake switch 21 is
switched to the T contact point 21T, the relay 24 is switched to
the "a" contact point 24a, and thus the solenoid 18a of the
solenoid controlled directional control valve 18 becomes connected
to the power source 23 and becomes excited. This opens the pilot
check valves 17 to utilize the hydraulic cylinders 2 as a
suspension system when the vehicle travels.
[0090] Next, the suspension operation achieved in the embodiment is
explained in further detail.
[0091] (1) Travelling mode
[0092] In the travelling mode, the brake switch 21 is switched to
the T contact point 21T as shown in FIG. 14. Thus, the solenoid 28
for working brake activation is demagnetized to release the working
brake and, at the same time, the solenoid 27 for parking brake
release is excited to release the parking brake. In addition, power
is supplied to the coil 25c of the relay 25 to switch the relay 25
to the "b" contact point 25b, which disconnects the circuit
extending to the solenoid 14a of the solenoid controlled
directional control valve 14 to demagnetize the solenoid 14a,
thereby setting the solenoid controlled directional control valve
14 to position (a). Furthermore, the circuit extending to the coil
26c of the relay 26 is cut off to switch the relay 26 to the "a"
contact point 26a and, at the same time, the circuit extending to a
coil 24c of the relay 24 is cut off to switch the relay 24 to the
"a" contact point 24a, thereby exciting the solenoid 18a and
ultimately setting the solenoid controlled directional control
valve 18 to position (b). It is to be noted that the solenoid 14a
becomes demagnetized and the solenoid 18a becomes excited in the
travelling mode, independently of the operation of the leveling
switch 22.
[0093] When the solenoid 14a is demagnetized as described above in
the hydraulic circuit shown in FIG. 11, the solenoid controlled
directional control valve 14 is switched to position (a) to allow
the pilot port 12a of the hydraulic pilot controlled directional
control valve 12 to communicate with the tank. As a result, the
hydraulic pilot controlled directional control valve 12 is switched
to position (a) and the P port of the directional control valve 8
becomes communicated with the tank. In addition, when the solenoid
18a is excited as the above, the solenoid controlled directional
control valve 18 is switched to position (b), thereby allowing the
pressure oil from the pilot hydraulic source 16 to be supplied to
the pilot ports of the pilot check valves 17. As the pilot check
valves 17 simply function as release valves, the pressure oil is
allowed to move between the head chambers 2b and the rod chambers
2c of the individual hydraulic cylinders 2 and the accumulator 7 to
achieve the suspension function.
[0094] In addition, in the travelling mode, the switching lever 8a
is switched to the neutral position shown in FIG. 9 with the
retaining cover 45 retaining the switching lever 8a at the neutral
position. Consequently, even if the switching lever 8a is subjected
to an impact due to a falling object, vibration or the like from
the ground surface while the vehicle is travelling, the switching
lever 8a retains the neutral state to prevent the pressure oil from
the directional control valve 8 from flowing out. In other words,
the vehicle height is not lowered due to an external impact while
the vehicle travels.
[0095] If a high-cycle vibration occurring as a result of, for
instance, the work vehicle travelling at high speed on a rough road
surface is input to the piston rods 2a via the tires 91 and the
axle 1 in the travelling mode described above, some of the pressure
oil (dynamic pressure oil) from the hydraulic cylinder 2 on the
high-pressure side (the contracting cylinder) travels to the
accumulator 7 via the restrictors 5a and 6a, to build up the
pressure of the pressure oil at the accumulator 7 and then the
pressure oil is supplied to the individual hydraulic cylinders 2 to
reset the body to the neutral position. At this time, the
accumulator 7 functions as a spring which absorbs the vibration of
the piston rods 2a, and firmer suspension is achieved as the gas
pressure in the accumulator 7 increases. In addition, the
restrictors 5a, 5b and 6a function as a damper which regulates the
communication of the vibration, and the hydraulic cylinders 2
engage in a stroking motion less readily as the sizes of the
restrictors become smaller to increase the damping performance.
Through the expansion/contraction of the hydraulic cylinders 2
which occurs as the pressure oil travels as described above, the
axle 1 is caused to move vertically or to rock relative to the
frame 70, and thus, even when an external force from the ground
surface is applied to the tires 91 while the vehicle travels, the
external force is not directly communicated to the frame 70. It is
to be noted that in this vehicle, the axle 1 moves vertically if,
for instance, an external force is applied to both the left tire 91
and the right tire 91 along the same direction and the left and
right hydraulic cylinders 2 expand/contract in the same direction,
whereas the axle 1 rocks if an external force is applied to only
either the left tire or the right tire and the left and right
hydraulic cylinders 2 expand/contract along directions opposite
from each other.
[0096] If a low-cycle vibration attributable to rough ground
surface is input to the piston rods 2a while the work vehicle
travels at low speed, the pressure oil (static pressure oil) is
supplied from the hydraulic cylinder 2 on the high-pressure side to
the hydraulic cylinder 2 on the low pressure side, thereby
equalizing the pressures at the individual hydraulic cylinders 2.
As a result, it becomes possible to sustain the grounding pressures
at the tires 91 at levels equal to each other even when the ground
surface is bumpy, to improve the stability of the work vehicle.
When the work vehicle is in a stationary state, the pressures at
the individual cylinders 2 become equal to each other to stop the
pressure oil flow, and the hydraulic cylinders 2 enter a stationary
state at a position at which the gravitational force W imparted
from the attachment 84 and the force F applied to the pistons 2p in
the hydraulic cylinders 2 are in balance (W=F). It is to be noted
that the force F applied to each piston 2p in this situation is
expressed as; F=P X (S1-S2), with S1 representing the area over
which the pressure is received at the piston 2p in the head chamber
2b, S2 representing the area over which the pressure is received at
the piston 2p in the rod chamber 2c and P representing the pressure
within the hydraulic cylinder 2.
[0097] Now, the displacement of the frame 70 relative to the axle 1
is explained in reference to an example. Let us assume that the
vehicle height is adjusted to align the central line 70L of the
frame 70 with the central line 1L of the axle 1 as shown in FIG. 5
in the initial state. If the left and right wheels are subject to
impact at the same time in this state and the hydraulic cylinders 2
contract as a result, the link 4 rotates around the pin 93, as
shown in FIG. 15A to shift the central line 70L of the frame 70 to
the left relative to the central line 1L of the axle 1. If the
hydraulic cylinders 2 expand, on the other hand, the central line
70L of the frame 70 becomes shifted to the right relative to the
central line 1L of the axle 1 as shown in FIG. 15B. While a side
surface of the frame 70 is set closer to the hydraulic cylinder 2
if the central line 70L of the frame 70 and the central line 1L of
the axle 1 become misaligned from each other in this manner, the
hydraulic cylinders 2 are mounted so that their axes 2L form an
A-line shape in the initial state as shown in FIG. 5 to prevent any
interference from occurring between the side surface of the frame
70 and the hydraulic cylinder 2.
[0098] (2) Parking Mode
[0099] In the parking mode, the brake switch 21 is switched to the
P contact point 21P as shown in FIG. 14. As a result, the solenoid
27 for parking brake release and the solenoid 28 for working brake
activation both become demagnetized, which engages the parking
brake and releases the working brake. If the leveling switch 22 is
turned off (opened) at this time, the solenoid 14a of the solenoid
controlled directional control valve 14 is demagnetized and, at the
same time, the circuit extending to the coil 24c of the relay 24 is
disconnected to switch the relay 24 to the "a" contact point 24a
and ultimately to demagnetize the solenoid 18a of the solenoid
controlled directional control valve 18.
[0100] As illustrated in FIG. 11, the electromagnetic switching
valves 14 and 18 are both switched to position (a) when the
solenoids 14a and 18a are demagnetized. Thus, the hydraulic pilot
controlled directional control valve 12 is switched to position
(a), the P port of the directional control valve 8 becomes
communicated with the tank and the pressure oil supplied to the
pilot ports of the pilot check valves 17 is stopped, thereby
allowing the pilot check valves 17 to function as check valves to
prohibit any movement of the pressure oil from the oil chambers 2b
and 2c of the individual hydraulic cylinders 2. In other words,
even if the switching lever 8a is operated with retaining cover 45
removed while the leveling switch 22 is in an OFF state, the
supply/discharge of the pressure oil to/from the hydraulic
cylinders 2 is prohibited and thus, the vehicle height does not
fluctuate in an undesirable manner.
[0101] While the vehicle can be adjusted to a desired height in
correspondence to the type of the attachment 84 in use, this
adjustment is implemented in the parking mode in the embodiment.
The following is an explanation of the height adjustment (leveling
operation). It is assumed that under the initial conditions, an
attachment 84 with standard weight w is mounted and each piston 2p
is in a stationary state at the position at which the allowable
stroke distances L1 and L2 for the hydraulic cylinder 2 along the
contracting direction and the expanding direction are equal to each
other (L1=L2) as shown in FIG. 16A. If the attachment 84 is
replaced with an attachment 84' with weight W' (>W), the
hydraulic cylinders 2 contract to lower the vehicle height at the
front, resulting in reduced allowable stroke distance L1'
(L1'<L1) along the contracting direction as shown in FIG. 16B.
If, on the other hand, the attachment 84 is replaced with an
attachment 84" with weight W" (<W ), the hydraulic cylinders 2
expand to increase the vehicle height at the front, resulting in a
reduced allowable stroke distance L2 "(L2"<L2) along the
expanding direction, as shown in FIG. 16C. As described above, when
the attachment 84 is replaced, the vehicle height becomes reduced
or increased, which results in a smaller allowable stroke distance
L1" or L2" in the contracting direction or the expanding direction,
and since the suspension function cannot be fully effected under
such circumstances, the comfort of the operator is compromised.
This may be prevented by sustaining a suitable vehicle height.
(e.g., L1'=L2', L1"=L2") when the attachment 84 is replaced through
a leveling operation. In the embodiment, if it is in the state of
the suitable vehicle height described above, the height of the
projections 73b provided at the front plate 73 of the frame 70 is
set equal to the height of the nipple 94a at the head of the pin 94
of the axle 1 (see FIG. 3).
[0102] Since the brake switch 21 is switched to the P contact point
21P, no power is supplied to the coils 25c and 26c of the relays 25
and 26, thereby switching the relays 25 and 26 to the (a) contact
points 25a and 26a respectively in the parking mode, as illustrated
in FIG. 14. If the leveling switch 22 is turned on (closed) to
perform a leveling operation in this state, the solenoid 14a of the
solenoid controlled directional control valve 14 becomes excited
and power is supplied to the coil 24c of the relay 24 to switch the
relay 24 to the "b" contact point 24b, thereby exciting the
solenoid 18a of the solenoid controlled directional control valve
18.
[0103] As shown in FIG. 11, when the solenoids 14a and 18a are
excited, both the solenoid controlled directional control valves 14
and 18 are switched to position (b). In addition, a locking
operation is performed at the gate lock lever 86 to switch the lock
valve 15 to position (b) when performing a leveling operation. As a
result, the pressure oil from the pilot hydraulic source 16 is
supplied to the pilot port 12a of the hydraulic pilot controlled
directional control valve 12, switching the hydraulic pilot
controlled directional control valve 12 to position (b), and, in
addition, the pressure oil from the pilot hydraulic source 16 is
also supplied to the pilot ports of the pilot check valves 17 to
utilize the pilot check valves 17 as release valves.
[0104] In this situation if, for instance, the hydraulic cylinders
2 are in the state shown in FIG. 16B (L1'<L2'), i.e., if the
height of the projections 73b provided at the front plate 73 of the
frame 70 is smaller than the height of the nipple 94a provided at
the end of the pin 94 at the axle 1 and, therefore, the hydraulic
cylinders 2 must expand to achieve a state in which L1'=L2', the
operator inserts his hand in the clearance between the side plate
71 and the tire 91 at the right front of the frame 70 to remove the
retaining cover 45 by loosening the wing nuts 46. Then, the
operator turns the switching lever 8a toward the A position in FIG.
9 to switch the directional control valve 8 to position (a). As a
result, the pressure oil from the main hydraulic source 13 is
supplied to the oil chambers 2b and 2c of the individual hydraulic
cylinders 2 via the directional control valve 8, which increases
the force F applied to the pistons 2p (the force applied in the
expanding direction) to expand the hydraulic cylinders 2, resulting
in an increase in the vehicle height.
[0105] If, on the other hand, the hydraulic cylinders 2 are in the
state shown an FIG. 16C (L1">L2"), i.e., if the height of the
projections 73b provided at the front plate 73 of the frame 70 is
greater than the height of the nipple 94a provided at the end of
the pin 94 of the axle 1 and thus, the hydraulic cylinders 2 must
contract to achieve a state in which L1"=L2", the switching lever
8a is turned toward the B position in FIG. 9 to switch the
directional control valve 8 to position (c). This causes the
pressure oil from the oil chambers 2b and 2c at the individual
hydraulic cylinders 2 to be discharged into the tank via the
directional control valve 8, which results in a reduction in the
force F applied to the pistons 2p to contract the hydraulic
cylinders 2, thereby reducing the vehicle height. When the height
of the projections 73b is set equal to the height of the nipple 94a
by increasing or decreasing the vehicle height in this manner,
i.e., when L1'=L2' or L1"=L2" is achieved, the switching lever 8a
is turned to the neutral position to switch the directional control
valve 8 to position (b). Then, the retaining cover 45 is mounted to
ensure that the switching lever 8a is not inadvertently
operated.
[0106] (3) Working Mode
[0107] In the working mode, the brake switch 21 is switched to the
W contact point 21W. In response, the solenoid 28 for working brake
activation becomes excited and the solenoid 27 for parking brake
release becomes demagnetized, thereby engaging both the working
brake and the parking brake. In addition, no power is supplied to
the coil 25c of the relay 25, switching the relay 25 to the "a"
contact point 25a, and power is supplied to the coil of the relay
26, switching the relay 26 to the "b" contact point 26b. As a
result, the solenoid 18a of the solenoid controlled directional
control valve 18 is not excited even if power is supplied to the
coil 24c of the relay 24 due to an erroneous operation of the
leveling switch 22, and thus, the solenoid controlled directional
control valve 18 is switched to position (a) to allow the pilot
check valves 17 to function as check valves. Consequently, the
vehicle height is not allowed to fluctuate even when the leveling
switch 22 is operated erroneously.
[0108] In addition, the following interlocking system is adopted in
the embodiment to further improve safety performance. If the
leveling switch 22 is turned on by mistake, the solenoid 14a of the
solenoid controlled directional control valve 14 becomes excited to
switch the solenoid controlled directional control valve 14 to
position (b). However, since a locking operation is performed at
the gate lock lever 86 in the working mode, the lock valve 15 is
switched to position (a) and thus, no pressure oil is supplied to
the pilot port 12a of the hydraulic pilot valve 12, allowing the P
port of the directional control valve 8 to communicate with the
tank. While the retaining cover 45 is mounted in the working mode
to prevent the switching lever 8a from shifting from the neutral
position, the pilot check valve 17 function as check valves as
explained above and the P port of the directional control valve 8a
communicates with the tank even if the switching lever 8 should
depart from the neutral position so that any movement of the
pressure oil from the oil chambers 2b and 2c of the hydraulic
cylinders 2 is prohibited with a high degree of reliability.
[0109] The pressure oil from the pilot hydraulic source 16 is
supplied to the work pilot valve (not shown) via the lock valve 15
in working mode, if an operating lever (not shown) is operated to
drive the attachment 84, for instance, the pilot pressure on oil is
guided to a pilot control valve in a quantity that is in proportion
to the degree to which the operating lever has been operated to
operate the control valves, thereby enabling an operation such as
excavation. Since any movement of the pressure oil from the oil
chambers 2b and 2c of the hydraulic cylinders 2 is prohibited at
this time, the hydraulic cylinders 2 do not engage in any stroke
motion and, consequently, the reactive force (excavation reactive
force) attributable to the excavating motion is not absorbed by the
accumulator 7, allowing the operation to be performed in a stable
manner in a suspension locked state.
[0110] In addition, since the mounting tolerance of the link 4
along the forward/backward direction (the clearance along the
forward/backward direction) is set smaller than the mounting
tolerance for the hydraulic cylinders 2 along the forward/backward
direction (the play in the forward/backward direction), the load
applied from the attachment 84 in the forward/backward direction is
communicated to the link 4, and thus, no load is applied to the
hydraulic cylinders 2 along the forward/backward direction. As a
result, the hydraulic cylinders 2 are protected. In this structure,
since the link 4 is formed in a box shape and the reinforcement
plates 4b are provided outside the main plates 4a, the flexural
rigidity and the torsional rigidity of the link 4 are improved to
assure a sufficient strength to withstand the excavating load.
[0111] The advantages achieved in the embodiment adopting the
structure described above are now explained.
[0112] (1) Since the frame 70 and the axle 1 are linked via the
pair of hydraulic cylinders, i.e., the left and right hydraulic
cylinders 2, and a single link 4, any impact imparted from the axle
1 while the vehicle travels is absorbed to allow the axle 1 to move
vertically or to rock in a smooth manner relative to the frame 70.
In addition, since the rod chambers 2c and the head chambers 2b of
the hydraulic cylinders 2 are made to communicate with the
accumulator 7 via the restrictors 5a, 5b and 6a, the shock
occurring when the hydraulic cylinders 2 expand/contract can be
absorbed effectively.
[0113] (2) Since the hydraulic cylinders 2 are supported by
adopting the trunnion system, the entire length (TL in FIG. 6) of
the cylinder tubes can be reduced, which makes it possible to
create extra space for storage between the cylinder tubes and the
swiveling body 83. In addition, since each hydraulic cylinder 2 is
connected with the bracket 3 via the projections 2t provided at the
cylinder tube, the width WL extending along the forward/backward
direction can be reduced (WL<WL') compared to the width of a
hydraulic cylinder having pins 53 inserted at the projections 2t of
the cylinder tube and linked with the bracket 3 via the pins 53, as
shown in FIG. 17. Furthermore, since the position of the bracket 3
is set with the knock pins 52, it can be prevented that the
projections 2t of the hydraulic cylinder 2 one-sidedly come into
contact with the inner walls of the openings 3a of the bracket 3.
Moreover, since the hydraulic cylinders 2 are installed by ensuring
that their axes 2L form an A-line shape (Japanese
character""shape), the hydraulic cylinders 2 and the frame 70 do
not interfere with each other when the hydraulic cylinders 2
expand/contract.
[0114] (3) Since the restrictor 5b provided at the passage C1
communicating between the head chamber 2b and the rod chamber 2c of
each suspension hydraulic cylinder 2 is a variable restrictor, the
suspension performance, in particular the damping performance, can
be adjusted with ease. In addition, the degree of firmness of the
suspension can be adjusted with ease even while the vehicle travels
with the center of gravity shifted to the rear due to the front
attachment turned to the rear. Furthermore, since the drain oil
from the pair of pilot check valves 17A and 17B internally provided
in the block IB which also includes the variable restrictor VD and
is mounted as an integrated part of each suspension hydraulic
cylinder 2 can be returned to the tank via a single drain port P5
provided at the block IB, the drain line can be simplified.
[0115] (4) In the hydraulic circuit in which the vehicle height is
adjusted by controlling the supply/discharge of the pressure oil
to/from the hydraulic cylinders 2, the function of a switching
valve for selecting supply/discharge of the pressure oil and the
function of a stop valve for cutting off the hydraulic cylinders 2
from the hydraulic pump 13 and the tank are both realized in the
ball-type three-position directional control valve 8, any leak of
the pressure oil from hydraulic cylinders 2 can be prevented with a
high degree of reliability to ensure that the vehicle height does
not change in an undesirable manner as long as the directional
control valve 8 is switched to the neutral position. In addition,
by providing the retaining cover 45 to retain the switching lever
8a for switching the directional control valve 8 at the neutral
position, the switching valve 8 can be retained at the neutral
position at all times (the function of a stop valve), thereby
ensuring that the leak of the pressure oil from the hydraulic
cylinders 2 and the quantity of the pressure oil supplied to the
hydraulic cylinders 2 are minimized.
[0116] (5) Since the directional control valve and the stop valve
are realized in a single valve, a compact system is achieved. In
addition, since the metering capability (flow regulating
performance) that reflects the degree to which the ball 8c
internally provided at the body 8b is operated is achieved, a
smoother movement of the upper swiveling body 83 is achieved during
a leveling operation. Furthermore, since the ball-type
three-position directional control valve 8 is provided at the
downstream side of the center joint 11, i.e., since the directional
control valve 8 is provided in close proximity to the accumulator 7
and the hydraulic cylinders 2, the hydraulic piping length (more
specifically, the length of the line 9) connecting the stop valve 8
and the accumulator 7 is reduced, which makes it possible to reduce
the extent to which the piping length affects the suspension
performance mainly designed in conformance to the capacity of the
accumulator 7. Since the line 9 is constituted of rubber hose in
the embodiment, the suspension performance is expected to
deteriorate due to an elastic deformation attributable to the high
pressure. Accordingly, a rubber hose achieving pressure
withstanding performance (e.g., 34.3 MPa) which is higher than the
maximum pressure (e.g., 8.8 MPa) of the suspension hydraulic
circuit by an ample margin is used to prevent the suspension
performance from deteriorating by minimizing the degree of elastic
deformation.
[0117] (6) Since the height of the diaphragm-type accumulator 7
provided in the middle of the line 5 communicating between the
hydraulic cylinders 2 is smaller than the height of a bladder-type
hydro-pneumatic accumulator achieving the same capacity, the
accumulator 7 can be installed with a high degree of efficiency (by
effectively utilizing the available space) within the space formed
by the right and left side plates 75 and 76 and the upper plate 77.
In addition, since the accumulator 7 is horizontally installed, it
is not necessary to draw out the line 6 connected to the
accumulator 7 in the downward direction, and thus the overall
height of the accumulator 7, which includes the line 6, can be
reduced.
[0118] (7) Since the switching valves 12, 14 and 15 that are
switched by interlocking with the operation of the brake switch 21
and the gate lock lever 86 are provided and the pressure oil is
supplied to the P port of the directional control valve 8 only when
the parking brake is engaged and the gate lock lever 86 is set at
the lock position (a work prohibited state), i.e., only when the
parking mode is selected, to allow of the vehicle height to be
adjusted through an operation of the switching lever 8a, no
leveling operation is performed when the vehicle is travelling or
is engaged in work. As a result, it is not necessary to consider
the leveling function while the vehicle is travelling, to simplify
the settings at the various cylinders involved in achieving the
suspension performance. At the same time, since any movement of the
pressure oil from the oil chambers 2b and 2c of the hydraulic
cylinders 2 is prohibited by the check valves 17 during a work
operation, the operator is able to feel the excavation reactive
force while working without any extraneous reactions. In addition,
since the relay circuit constituted of the brake switch 21, the
relays 24.about.26. and the like prohibit a leveling operation
(so-called interlocking) even when the leveling switch 22 is turned
on by mistake while the vehicle is travelling or is engaged in work
or even when the switching lever 8a is operated during work without
mounting the retaining cover 45 (the switching lever cannot be
operated while the vehicle is travelling), no undesirable leveling
operation is performed. Furthermore, since a leveling operation is
prohibited while the vehicle is travelling or engaged in work, the
pressure oil from the main hydraulic source 13 is not utilized for
frequent control of the pressure at the hydraulic cylinders 2,
thereby achieving a reduction in fuel consumption.
[0119] (8) With the switching lever 8a that drives the ball-type
three-position directional control valve 8 projecting out to the
side of the vehicle from the side plate 71 of the frame 70 and the
fender 61F covering the switching lever 8a from the front, and
above relative to the vehicle, the switching lever 8a is protected
from falling objects and the like. In addition, since the switching
lever 8a is set further frontward in the vehicle relative to the
hydraulic cylinders 2 located directly above the axle 1, the
operator does not need to insert his hand into a deep recess to
improve the operability, and can perform a leveling operation with
ease and reliability by visually checking any positional changes
occurring with regard to the hydraulic cylinders 2 and the link 4
from the front of the vehicle. Moreover, by providing the notched
portion 73c having the projections 73b at the front plate 73 of the
frame 70, it becomes possible to visually check the positional
relationship between the projection 73b and the pin 94 from the
front of the vehicle to achieve a fine adjustment of the vehicle
height with ease and also, the ease of assembly work for linking
the axle 1 and the frame 70 and the ease of maintenance are
improved. In addition, the structure is simplified since the
control device for leveling and the like are not required to
achieve a reduction in the production cost.
[0120] -Second Embodiment-
[0121] FIG. 18 is a hydraulic circuit diagram illustrating the
structure of the leveling device achieved in the second embodiment
of the present invention. It is to be noted that the same reference
numerals are assigned to components identical to those shown in
FIG. 11 and the following explanation mainly focuses on the
differences from FIG. 11. As shown in FIG. 18, the leveling device
in the second embodiment is constituted by providing an solenoid
control valve 31 that controls the flow of the pressure oil from
the main hydraulic source 13 to the individual hydraulic cylinders
2, a controller 30 that controls the drive of the solenoid control
valve 31, stroke sensors 32 and 33 that detect the stroke distances
z1 and z2 of the hydraulic cylinders 2 from a reference position z0
(corresponds to the state shown in FIG. 16A in the embodiment) and
a gate lock switch 86a that is turned on/off in response to a
release/lock operation of the gate lock lever 86, in place of the
directional control valve 8, the hydraulic pilot controlled
directional control valve 12, the lock valve 15 and the solenoid
controlled directional control valve 14 in FIG. 11 and the relay
circuit in FIG. 14. It is to be noted that although not shown, the
solenoid 27 for parking brake release and the solenoid 28 for
working brake activation are connected to the brake switch 21, as
illustrated in FIG. 11.
[0122] The stroke sensors 32 and 33, the gate lock switch 86a, the
brake switch 21 and the leveling switch 22 are connected to the
controller 30. The controller 30 executes the processing described
below based upon the signals input from them and outputs a control
signal I to solenoids 31a and 31b of the solenoid control valve 31
and the solenoid 18a of the solenoid controlled directional control
valve 18.
[0123] FIG. 19 is a flowchart of an example of the processing
executed by the controller 30. The processing in this flowchart is
started by, for instance, turning on the engine key switch (not
shown). First, a decision is made in step S1 as to which position
the brake switch 21 has been switched to based upon the signal
provided from the brake switch 21. If it is decided that the brake
switch 21 has been switched to the P contact point 21P, the
operation proceeds to step S2 to make a decision as to whether or
not the leveling switch 22 has been turned on. If an affirmative
decision is made in step S2, the operation proceeds to step S3,
whereas if a negative decision is made, the operation proceeds to
step S13. In step S3, a decision is made as to whether or not the
gate lock switch 86a has been turned on, i.e. whether or not a lock
operation has been performed at the gate lock lever 86. If an
affirmative decision is made in step S3, the operation proceeds to
step S4, whereas if a negative decision is made, the operation
proceeds to step S11. In step S4, the control signal I is output to
the solenoid 18a of the solenoid controlled directional control
valve 18 to excite the solenoid 18a. In response, the solenoid
controlled directional control valve 18 is switched to position (b)
as shown in FIG. 18, and the pressure oil from the pilot hydraulic
source 16 is supplied to the pilot ports of the pilot check valves
17 to enable the pilot check valves 17 to function as release
valves.
[0124] Next, the detection values z1 and z2 obtained at the stroke
sensors 32 and 33 are read in step S5. In step S6, the average
((z1+z2)/2) of the detection values z1 and z2 is ascertained and
then the deviation "a" (=za-(z1 and z2)/2) is calculated by
subtracting the average from a predetermined target value Za (e.g.,
0, which represents the state in which L1=L2). Next, a decision is
made instep S7 as to whether or not the deviation "a" is larger
than a predetermined upper limit value al (e.g., 1.01.times.a), and
the operation proceeds to step S8 if an affirmative decision is
made, whereas the operation proceeds to step S9 if a negative
decision is made. In step S8, the control signal I is output to the
solenoid 31a of the solenoid control valve 31 to excite the
solenoid 31a and then the operation returns to step S5. Thus, the
solenoid control valve 31 is switched to position (a), allowing the
pressure oil from the main hydraulic source 13 to be supplied to
the oil chambers 2b and 2c of the hydraulic cylinders 2. As a
result, the hydraulic cylinders 2 expand to raise the vehicle
height. In step S9, a decision is made as to whether or not the
deviation "a" is smaller than a predetermined lower limit value a2
(e.g., 0.99.times.a), and the operation proceeds to step S10 if an
affirmative decision is made, whereas the operation proceeds to
step S11 if a negative decision is made. In step S10, the control
signal I is output to the solenoid 31b of the solenoid control
valve 31 to excite the solenoid 31b, and then the operation returns
to step S5. As a result, the solenoid control valve 31 is switched
to position (c), allowing the pressure oil from the hydraulic
cylinders 2 to be discharged into the tank. This causes the
hydraulic cylinders to contract, which, in turn, lowers the vehicle
height. In step S11, the output of the control signal I to the
solenoids 31a and 31b of the solenoid control valve 31 is stopped
to demagnetize the solenoids 31a and 31b, before the operation
makes a return. Consequently, the electromagnetic control valve 31
is switched to position (b), which cuts off the circuit on the side
of the hydraulic cylinders 2 from the main hydraulic source 13 and
the tank.
[0125] If it is decided in step S1 that the brake switch 21 has
been switched to the T contact point 21T, the operation proceeds to
step S12, in which the control signal I is output to the solenoid
18a of the solenoid controlled directional control valve 18 to
excite the solenoid 18a before proceeding to step S11. As a result,
the solenoid controlled directional control valve 18 is switched to
position (b) to allow the pressure oil from the pilot hydraulic
source 16 to be supplied to the pilot ports of the pilot check
valves 17 so that the pilot check valves 17 function as release
valves. Thus, the oil chambers 2b and 2c of the hydraulic cylinders
2 become communicated with the accumulator 7, thereby effecting the
suspension function (a suspension unlocked state) to absorb and
damp the vibration occurring while the vehicle travels. If it is
decided in step S1 that the brake switch 21 has been switched to
the W contact point 21W, the operation proceeds to step S13 in
which the output of the control signal I to the solenoid 18a of the
solenoid controlled directional control valve 18 is stopped to
demagnetize the solenoid 18a before proceeding to step S11. In
response, the solenoid controlled directional control valve 18 is
switched to position (a) to stop the supply of the pressure oil to
the pilot ports of the pilot check valves 17, thereby allowing the
pilot check valves 17 to function as check valves. As a result, the
inflow/outflow of the pressure oil to/from the oil chambers 2b and
2c of the hydraulic cylinders 2 is prohibited (a suspension locked
state), in order to resist the excavating reactive force and the
like.
[0126] It is to be noted that since specific features of the basic
operation achieved in the second embodiment are identical to those
in the first embodiment, including the suspension function effected
by the accumulator 7 in the travelling mode, a leveling operation
enabled when the parking brake is engaged and a lock operation is
performed at the gate lock lever 86 in the parking mode and the oil
chambers 2b and 2c of the hydraulic cylinders 2 cut off in the
working mode, a detailed explanation of these features is
omitted.
[0127] In the second embodiment, in which the vehicle height is
automatically adjusted by switching the solenoid control valve 31
in response to a command from the controller 30 based upon the
detection values z1 and z2 provided by the stroke sensors 32 and 33
as described above, the directional control valve 8 does not need
to be operated manually, to achieve a simpler operational
procedure, thereby improving the efficiency of the leveling
operation.
[0128] In the explanation given above, a block IB having the
variable restrictor VD provided at the passage C1 between the head
chamber 2b and the rod chamber 2c is provided in conjunction with
each suspension hydraulic cylinder 2, to adjust the suspension
performance. As an alternative, the pilot check valves 17A and 17B
provided in conjunction with each hydraulic cylinder 2 may be made
to communicate with each other via a rubber hose GH with a
restrictor 5b provided at a connection adaptor AD provided to
connect the rubber hose GH to enable suspension performance
adjustment by replacing the adapter with any of the various
adapters with different internal diameters. The suspension
performance and, in particular, the firmness can also be adjusted
with ease by constituting the restrictor 5a provided between the
head chamber 2b of each suspension hydraulic cylinder 2 and the
accumulator 7 with a variable restrictor. The alternative described
earlier may also be adopted in this structure, by connecting the
head chamber 2b of the suspension hydraulic cylinder 2 and the
accumulator 7 with a rubber hose, providing the restrictor 5a at
the connection adapter and replacing the adapter with any of
various adapters with different internal diameters to achieve
suspension performance adjustment. While the restrictor 5b is a
variable restrictor in the embodiment, the restrictor 5b may be a
fixed restrictor and the restrictor 5a, instead, may be constituted
as a variable restrictor. Alternatively, by constituting both the
restrictor 5b and the restrictor 5a as variable restrictors, the
damping performance and the firmness can both be adjusted with
ease.
[0129] In addition, while the entire accumulator 7 is housed within
the space formed by the upper plate 77 and the side plates 75 and
76 of the frame 70 in the explanation given above, the accumulator
7 does not need to be housed inside the space in its entirety,
since it will be protected from falling objects and the like as
long as most of the accumulator 7 is housed inside. While the
accumulator 7 is horizontally installed inside the frame 70, it may
be vertically installed or diagonally installed instead.
[0130] In the embodiments explained above, the directional control
valve function which allows the hydraulic cylinders 2 provided for
leveling and suspension to be connected to the hydraulic pump 13 or
the tank and the stop valve function which minimizes the leak by
cutting off the hydraulic cylinders 2 from the hydraulic pump 13
and the tank are realized in a single ball-type three-position
directional control valve 8. However, if a spool-type
three-position directional control valve such as that disclosed in
Japanese Laid-Open Patent Publication No. H 7-132723 is employed to
minimize fluctuations in the vehicle height by preventing the leak
at the hydraulic cylinders for leveling and suspension with a high
degree of reliability, a stop valve achieving a structure that
minimizes the leak may be provided in series to the spool-type
three-position directional control valve. The spool-type
three-position directional control valve disclosed in Japanese
Laid-Open Patent Publication H7-132723 is provided between a line
connecting an accumulator with a hydraulic cylinder and a hydraulic
source. The spool-type three-position directional control valve is
driven according to a clearance between a vehicle body and-an axle,
which is detected by a distance meter, to supply/discharge pressure
oil from the hydraulic source to/from the hydraulic cylinder. In
this manner, the distance between the vehicle body and the axle is
set to a specified value to keep the work vehicle level. Such a
stop valve may be the ball-type switching valve shown in FIG. 12, a
pilot type check valve that functions as a release valve or a check
valve in correspondence to the level of the pressure applied to the
pilot port, or the like.
[0131] In addition, while the position of the switching lever 8a is
restricted by securing the retaining cover 45 with the wing nuts 46
in the embodiments described above, the switching lever 8a may be
retained at a specific position through another method. FIGS. 21A
and 21B present examples of methods that may be adopted for this
purpose. In the method shown in FIG. 21A, a hinged plate 47 capable
of swinging along the direction indicated by the arrow AB around a
rotational axis AX constituting the support point is provided, and
a spring (not shown) is mounted inside a rotating member 47a. This
spring applies a force to the hinged plate 47 along direction B,
thereby restricting the position of the switching lever 8a. In the
method shown in FIG. 21B a pair of arched guides 71b are secured at
the side plate 71, a thin plate 48 capable of sliding along the
direction indicated by the arrow AB are inserted inside the guides
71b and the thin plate 48 and the side-plate 71 are linked with
springs 49. These springs 49 apply a force to the plate 48 along
direction B, thereby restricting the position of the switching
lever 8a.
[0132] While the projections 73b are provided at specific positions
(positions corresponding to the position of the nipple 94a) at the
front plate 73 of the frame 70 to facilitate a leveling operation,
a mark other than such projections (e.g., scribing) may be
provided. In addition, while the accumulator 7 communicates with
the right and left hydraulic cylinders 2, separate accumulators 7
may be provided for the individual hydraulic cylinders 2. While the
leveling device is provided only in conjunction with the front
wheels in the embodiment described above, the leveling device may
be provided only in conjunction with the rear wheels or in
conjunction with both the front wheels and the rear wheels.
Moreover, while the state of the vehicle, i.e., the travelling
state, the park state or the working state, is detected in response
to an operation of the brake switch 21, i.e., in correspondence to
the braking state, in the embodiments described above, the state of
the vehicle may instead be detected based upon a detection value
provided by a vehicle speed sensor (not shown) or the like.
[0133] Industrial Applicability
[0134] While an explanation is given above on an example in which
the present invention is adopted in a wheeled hydraulic excavator,
the present invention may be likewise adopted in other types of
wheeled work vehicles.
* * * * *